Hi Helena,
I was away at IPC Works and am just catching up on tech-net, sorry for the delay.
As with all things there are different opinions. I don't believe I can 100% agree with some of the comments previously made.
Here is what I have experienced.
I have been measuring the reliability of bare printed wire board (PWBs) by thermal cycling representative coupons and am limiting this reply primarily to bare boards.
Delamination increases thermal cycles to failure by distressing the boards internally and reducing and/or limiting the magnitude of separations (barrel cracks) about 90% of the time. The coupons that fail in 300 cycles may become unbreakable in 1000 thermal cycles (150C) after the onset of delamination.
About 10% of the time delamination reduces thermal cycles to failure by focusing stress into the barrel of the plated through hole (PTH). Though not common, this type of delamination may reduce thermal cycles to failure by greater than 50%.
The are two major types of delamination, cohesive (material failure, chemical), adhesive (surface to surface failure, mechanical).
There is also a condition that some call "crazing" where there are microscopic cracks, or separations, that develop between the resin and the fiberglass. Although this is generally not considered delamination, it is a micro-delamination of sorts. Crazing is associated with conductive anionic filament growth (CAF).
There are many subtypes of delamination including, blistering, eyebrow, butterfly, donut, vertical, horizontal, laminate voids, stress cracks, pink ring, soda strawing, prepreg void, resin cracks, fiber bundle cracks, gross wicking etc. These different names are colloquial and mean different things in different companies.
Recently there has been a lot of talk about cratering resulting from X/Y coefficient of thermal expansion (CTE) mismatches between the PWB and components and also pad rotation due to z-axis expansion. Cratering may be propagated by vibration and physical shock tests or thermal cycling. Cratering appears to be a cohesive delamination.
Lead-free processing (assembly and rework, and preconditioning to simulate lead-free processing, is increasing the incidence and magnitude of delamination.
There is always "spec-man-ship" discussions about this is the condition "delamination" or "non-lamination" and can a you have "delamination" in a part or sub composite that was never been laminated to begin with...
Here at PWB Inc. we are beginning to detect delamination electrically in our reliability coupons.
Paul Reid
PWB Interconnect Solutions
613 596 4244 ext 229
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Pasquito, Helena
Sent: Tuesday, September 12, 2006 12:45 PM
To: [log in to unmask]
Subject: [TN] Delamination
Hi TechNetters,
Let me ask a question; I know delamination is bad, but why? What is the
failure mode to the board when a board delaminates and would there ever
be an instance that a board that delaminates is still OK to use? This
is a Class 3 application. Yes, I know what the IPC standards say but
not real sure about the board process. Yes, I "googled" and there is a
lot of stuff out there. Maybe someone can recommend some reading
material (hopefully short and sweet and to the point).
Thanks!
Helena
Helena Pasquito
Manufacturing Skills Instructor
M/A-COM, Tyco Electronics
1011 Pawtucket Blvd., M/S 107
Lowell, MA 01853
978-442-5024
[log in to unmask]
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